In the history of automotive vehicles, the furnishing of fuel to the internal combustion engines has had an interesting progression. In the early days, the fuel was fed to the carburetors by a gravity feed system using the vacuum of the manifold. Later, a fuel pump was added in the engine compartment and operated by a rotating cam to pull fuel from the rear fuel tank to the engine carburetor. A later development was the use of a fuel pump driven by an electric motor powered by the vehicle battery. Subsequently, the electrical pumps were developed to be totally enclosed and the pumps were then located in the main fuel tank of the vehicle, usually at the rear of the vehicle. In this location, the fuel system was provided with a pressure regulator wherein, when the fuel demand of the engine was not utilizing the full capacity of the pump, the increased pressure in the fuel line was sufficient to cause the regulator to dump excess fuel into a return line where it was fed back to the main fuel tank.
This pressure regulator return proved to have disadvantages because the return fuel absorbed heat and carried it back to the main fuel tank where it raised the temperature of the main fuel supply. This problem was partially alleviated by installing the fuel pump in a cylindrical upright reservoir within the main fuel tank and directing the return fuel back to the reservoir where it was isolated from the main fuel supply.
The next progression involved the use of an electrical system in conjunction with the pump drive which eliminated the pressure regulator return line and provided for a pump speed regulation responsive to pump outlet pressure. This is described in a U.S. Pat. No. 4,728,264, to Charles H. Tuckey, issued Mar. 1, 1988. These pumps are utilized to deliver fuel to a fuel rail in which electronic fuel injection devices are provided at each engine cylinder to deliver fuel and air at timed intervals.
It will be appreciated that automotive vehicles must operate in many extremes of ambient temperatures. In southern and western states, the ambient temperatures many times may reach 100.degree. F. or higher. When a vehicle is sitting in the sun, especially after it has been operating, the temperatures in the engine compartment and the fuel rail may climb to well over 100.degree. F. Under these conditions, vapor will form in the in-fuel rail and the fuel injectors causing a "hot restart" and rough idle which is unsatisfactory.
An attempt has been made to eliminate this "hot start" problem in non-return systems by installing a check valve in the fuel line downstream from the regulating device. This traps fuel in the fuel rail which causes an immediate pressure rise in the fuel rail and injector area during "engine off" and "hot soak" conditions, that is, a temperature rise in the engine compartment. This pressure rise prevents vaporization but, because of this increase in pressure, a pressure relief valve was installed between the check valve and the fuel rail. One functional disadvantage, however, developed because the pressure regulator valve limits the pressure by dumping fuel. Also, upon restart, the pressure drops quickly to normal pump-regulated pressure but rough idling could result until temperatures normalized.
It is an object of the present invention to eliminate, under hot operating conditions and during restart, the rough idle or engine stumble while maintaining a non-return system and avoiding the bleeding off of fuel dumping. As will be described, this is accomplished by utilizing electric pump control while providing expansion storage capacity for an extended period, thus allowing fuel temperatures to fall before fuel pressure drops to a normal regulated system pressure.
It is a further object to provide a pressure responsive control unit which has a reference passage to an engine manifold land a responsive signal to control pulse width modulation of voltage to a fuel pump.
An overall object is the compensation in the system for high fuel rail temperatures to provide smooth idling and starting of an engine. A further object is the utilization of a heat responsive contact member in conjunction with an electronic circuit in an expansion storage unit in the pulse width modulation element.